Needles have always been an integral part of the warp knitting process. In the past different types of needles have been used in different machines. Two predominate types of warp knitting machines in use today are the Tricot machine and the Raschel machine. Historically, the Tricot machines used bearded needles in forming a warp knit, while Raschel machines only used latch needles. With the production of modern warp knitting machines, however, compound needles replaced bearded needles in Tricot machines and also penetrated into the Raschel machine market.
Compound needles allowed for faster production on a warp-knitting machine due to their unique construction making them more desirable to warp knit manufacturers using Tricot machines. A compound needle possesses two distinct parts which form the needle: the hooking element and the closing element, or closure blade. The hooking element and closing element of a compound needle work in concert to form the proper knit while having discrete movements within the warp-knitting machine during the knitting process.
The hooking element includes a hook, a stem and a butt. The hook is a curved member used to catch and hold the yarn being knitted into the warp knit. The stem extends from the hook down to the butt of the hooking element. The butt is used to hold and manipulate the hooking element within the warp-knitting machine. The hook, the stem and butt of the hooking element are aligned in such a manner that the curved portion of the hook is in the same plane as the stem and the butt. The stem of the hooking element possesses a groove on the side to which the hook of the hooking element is opened. The closing element includes a blade and a butt. The blade is on the working end of the closing element which interacts with the hooking element during the knitting process, while the butt aids in holding and manipulating the closing element within the warp knitting machine.
During the knitting process, the blade of the closing element operates within the groove in the stem and closes off the open end of the hook. Due to the small size of the needles, a low tolerance exists for the alignment of the closing elements and the hooking elements. The angle of the blade of the closing elements and the blades alignment with the groove in the stem of the hooking element need to be near perfect for proper operation of the warp-knitting machine and to prevent breakage of the needle parts. Further, a warp knitting machine uses many evenly spaced needles in close proximity to each other within the warp-knitting machine.
To increase efficiency and easy of maintenance, the closing elements are grouped together in closing elements assemblies usually in groups of 14, 16, and 18 per half inch. These closing element assemblies, usually called castings, are formed by having closing elements aligned in a caster with proper spacing and pitch. Molten tin then is poured into the caster encasing the butt end of the closing elements. The butt ends of the closing elements are immersed in the tin constituting the actual casting, while the working end is left exposed. The castings are then removed from the caster and further shaped and manipulated to ensure proper alignment for interacting with the hooking elements in the warp knitting machines. While the use of castings improve the efficiency of maintaining the warp-knitting machine, the closing element casting formation and use also produce a myriad of issues. These issues include precision problems, concerning true gauge, blade alignment and sizing, and weight issues within the operation of the warp knitting machines.
True Gauge is defined as the securing of individual closing elements in parallel positions to each other and at a specific, equal distance apart. Such positioning of the closing elements presents an elusive target for a casting for many reasons. Most significant is that the molten tin must undergo a phase change from liquid to solid during the casting process. The molten tin is poured into the casters at over 600° C. As the casting cools and shrinks, the closing elements' optimal positionings are disturbed within the caster, adversely affecting the true gauge. The closing elements often have to be manipulated back into a parallel and equidistant position.
Blade alignment is defined as the pitch or angle of the blade in the assembly. Just as with true gauge, blade alignment is a critical requirement, since the closing elements of each casting are running at close tolerances and high speeds in a large and complicated machine. The casting process often affects blade alignment as it affects true gauge. The blade portion of the closing elements must be manipulated with pliers and other tools to return them to their desired angle. This manipulation of the closing elements to produce the desired conformance for both true gauge and blade alignment causes a loosening of the closing elements within the cavity of the castings increasing the chance of failure of the casting when put into use.
Sizing is defined as the measurement requirements for the exterior of the castings in order to properly fit into the warp-knitting machine. Sizing presents another problem for the casting product. The castings must be held tight in the warp-knitting machine due to the precise nature of the interaction of the hooking element and the closing elements and the speed at which the machines operate. These operational necessities of the warp-knitting machine require precise specifications for the press, or thickness, of the castings and width of the castings. No raw casting can achieve this requirement. Therefore, the tin covering the butt end of the closing elements must be brought within the specification through a secondary manufacturing procedure call shaving.
In the shaving process, the casting manufacturers use special files and other tools to manually remove excess tin from the width (the sides and back of the casting surrounding the butt ends of the closing elements) and the thickness (the top and bottom of the casting surrounding the butt end of the closing elements) to bring the castings within the required specifications. The shaving processes often disturbs the blade positioning through handling, or through the application of force, requiring correction to achieve the true gauge and desired blade alignment. The manual shaving process is both time consuming and costly.
Another precision issue, which arises concerning the use of castings, is the inconsistency of the molding process. There are many molds used throughout the world that produce castings for use in warp knitting machine, and no two molds can exactly reproduce identical parts, sometimes causing a problem in a knitting machine. Having castings from different molds increase the handling time needed during the shaving process. Further, all casting molds deteriorate over time causing additional problems in the reproducibility of the castings from deteriorated molds and increasing the time and effort put forth in the manual shaving process.
A further concern in warp knitting operations that warp knitters are always looking to improve is the weight of component parts. The use of tin to create a solid base surrounding the butt ends of the closing elements within the castings creates a firm foundation which holds the closing elements in their proper position during the operation of the warp-knitting machine. However, in the same vein, the solid casting of tin adds excess weight to each casting. While each casting containing the closing elements is not a heavy component part, when considering the number of castings of closing elements used in a single warp knitting machine, the total weight of all the castings is not insignificant. When taking into consideration the high rate of speed at which the warp knitting machines operate, the force created by this gross weight grows exponentially. This force produced by the speed and weight creates additional stress and wear on the warp-knitting machine. Avoiding such additional stress and wear increases the life of the component parts running the warp knitting machines as well as the life of the warp knitting machines themselves.